Catalytic dehydrogenation of paraffins



Patented Nov. 20, 1951 CATALYTIC DEHYDROGENATION OF PARAFFIN S John W.Myers, Bartlesvilie, kla., assignor to Phillips Petroleum Company, acorporation of Delaware No Drawing. Application February 28, 1949,Serial No. 78,891

This invention relates to the catalytic dehydrogenation of parafilnhydrocarbons to produce olefins and diolefins. In one of its morespecific aspects it relates to an improved process for thedehydrogenation of aliphatic paraffin hydrocarbons in the presence ofsteam and steam insensitive alumina-metal oxide catalysts to produce thecorresponding olefins and diolefins and is particularly applicable tothe production of olefins and diolefins from aliphatic parafilnscontaining from four to five, carbon atoms per molecule. In thedehydrogenation of paraflins to the corresponding diolefins, twodehydrogenation steps are customarily employed. In the first step theparafiins are dehydrogenated to olefins which are then subjected in asecond step to a separate dehydrogenation treatment to producediolefins. The olefins may or may not be separated from the effluent ofthe first dehydrogenation step prior to dehydrogenation to dioleflns.

The customary procedure for the production of diolefins bydehydrogenation of corresponding parafiins involves separatedehydrogenation oi! parafiins and olefins using somewhat differentconditions for each dehydrogenation reaction. The paraffins are firstdehydrogenated to olefins in the presence of a highly activedehydrogenation catalyst, the olefins are separated from the eflluent ofthe paraffin dehydrogenation step, and separately converted to thecorresponding diolefin at a temperature somewhat higher and in thepresence of a less active dehydrogenation catalyst than employed for theparaffin dehydrogenation step. Chromium oxide is the activedehydrogenation catalyst conventionally used for the dehydrogenation ofparaflins but it is much too severe for olefin dehydrogenation. Separatedehydrogenation of parafiins and olefins requires the use of diflicultand relatively expensive separation steps to segregate the parafiin andolefin feed stocks, but the separation procedure is justified on thebasis of improved yields and operation. I

In the dehydrogenation of paraflins some diolefins are formed; however,the dehydrogenation of parafiins directly to diolefins is not practicalby present dehydrogenation processes. Attempted combinations ofconcurrent dehydrogenation reactions involved in converting paramns todiolefins in a single dehydrogenation step encounter serious diflicultydue to the fact that optimum conditions for the conversion of paraflinsto olefins are quite different from theoptimum conditions for theconversion of olefins to dioleflns.

8 Claims. (Cl. 260683.3)

For the dehydrogenation of paraffins, such as normal butane, thecatalyst ordinarily employed comprises approximately 10 weight per centchromium oxide (ClzOs) deposited on a suitable carrier, such as aluminumoxide. As might be expected from the law of mass action, thedehydrogenation reaction is favored by low absolute or partialpressures. Low absolute pressures, i. e., below atmospheric pressure,whilefavorable to the dehydrogenation reactions, are undesirable incommercial operations due to the difiiculty of preventing leakage of airinto the system. For

this reason it is customary to employ pressures somewhat aboveatmospheric pressure, generally in the neighborhood of about 30 poundsper square inch gage. A low partial pressure of the reactants, e. g.,normal butane, may be obtained by dilution with an inert gas; It hasbeen found that steam is undesirable as a diluent for thedehydrogenation of paraflins since it poisons or reduces the activityand life of the chromium oxide catalyst of the conventional type. Whileother gaseous diluents, such as propane and lighter hydrocarbons, arenot subject to this disadvantage they are generally not employed becausethe handling and recycling of large amounts of gaseous diluentsrepresents a large item in plant investment and operating cost. Thedehydrogenation of parafiins containing four or five carbon atoms permolecule may be conducted in the absence of a diluent with an efficientseparation of olefin products from the parafiin recycle stock.

From the standpoint of chemical and physical characteristics, the mostdesirable diluent for dehydrogenation is water vapor. This diluent maybe cheaply provided in any desired amount and may be removed from thehydrocarbon stream by simple condensation, thereby eliminating a largepart of the compression and fractionation equipment necessary when otherdiluents are used. Steam has been used as a feed diluent in severaldifferent types of catalytic and thermal processes for hydrocarbonconversion such as cracking and olefin dehydrogenation. In suchprocesses, particularly those in which solid catalysts are used, thesteam serves not only as a diluent, but also as a reagent for theremoval of carbon that deposits on the catalyst.

As mentioned hereinbefore, the use of water vapor has previously beencondemned in the art because of its deleterious effects on the activityof conventional catalysts employed for the dehydrogenation of paraflins.The catalysts now used for the dehydrogenation of parafiins incommercial operations show poor conversion when steam is used as adiluent. Present practice is to dehydrogenate undiluted paraflins or touse a feeds are, in many cases, substantially unreacted (see Schulze etal., U. S. 2,367,623)

Catalysts have recently been devised in contact with which paraflins maybe efiectively and efficiently dehydrogenated in the presence of majoramounts of steam, as is disclosed in application Serial No. 683,996, nowPatent No. 2,500,- 920, filed July 16, 1946, of' which I am one of thejoint inventors. The catalysts disclosed therein consist essentially ofa major proportion of alumina and minor amounts of one or more of theoxides of molybdenum, tungsten, and vanadium. It is also disclosed thatthese catalysts may be further improved by the addition of from 1 to 15weight per cent chromium oxide.

I have now found that catalysts consisting essentially of alumina andthe above enumerated dehydrogenating oxides, in which the alumina is inminor amount by weight of the composite catalyst, have substantiallylonger life than catalyst composites of the same constituents but inwhich the alumina is present in major proportions.

An object of this invention is to provide an improved process for theproduction of olefins and diolefins from corresponding parafiins.Another object of the present invention is to provide a process for thedehydrogenation of paraflins wherein steam or water vapor may beeffectively and efficiently employed as the diluent. A more .specificobject is to provide a process which is particularly applicable to thedehydrogenation of butane to produce butylenes and butadiene. It is alsoan object of the invention to provide catalysts for the conversion ofparaflins to olefins and diolefins in the presence of water vapor as adiluent, which catalysts maintain higher conversion activity for longerperiods of time than catalysts heretofore known. Still another object ofthe present invention is to provide catalysts which give efiicientconversion of parafllns to olefins and diolefins in the presence ofwater vapor as a diluent. Other'objects and advantages will becomeapparent to those skilled in the art from the accompanying disclosure ofthe invention.

It has been found that parafilns may be advantageously dehydrogenated inthe presence of steam as a diluent to produce olefins and diolefins.Advantages obtained by steam dilution are longer reaction cycles,obviation of the necessity for using reactors made of special heat andcorrosion resistant alloys, and the feasibility of using comparativelylarge reactors. The longer reaction cycles result from the chemicalreaction of steam on deposited carbon, known as the water gas reaction,which enables the catalyst to be used for long periods withoutregeneration with an oxygen-containing gas. Large reactors of the 'bedtype, in contrast to reactors comprising complex heat exchange systems,may be employed in this process as a result of the heat-carryingcapacity of steam. This represents a tremendous saving in investment andoperating costs.

It has also been found that catalysts that are 4 satisfactory for thedehydrogenation of undiluted parafflns are relatively unsatisfactory forthe dehydrogenation of paraflins diluted with steam because of lowyields and short process cycles. It has been further found that acatalyst containing a major portion of alumina and a minor proportion ofat least one oxide of the group molybdenum oxide, tungsten oxide, andvanadium oxide is satisfactory for dehydrogenating paranins diluted withsteam. The catalysts of the present invention consist essentially of aminor amount of alumina, preferably in the range of 10 to 45 per cent byweight of the composite and the balance at least one, and preferablymore than one, of the oxides of molybdenum, yanadium, and tungsten, eachin the amount of at least 5% of the weight-of the catalyst. While acatalyst of alumina and chromia alone is unsatisfactory fordehydrogenating in the presence of steam, it is desirable to incorporatefrom 1 to weight per cent, preferably 5 to 50 weight per cent, ofchromia in a catalyst composition of alumina and one of the oxides justnamed. Pieierred combinations of these dehydrogenating metals incombination with alumina are chromiavanadia, chromia-molybdena, andvanadia-molybdena. These catalysts are especially effective andefficient in the dehydrogenation of paraiiins diluted with steam inlargeamounts and have considerably longer life before regeneration isrequired than catalysts containing the same constituents with a majorproportion of alumina.

'i'he catalysts of this invention may be prepared by any of the methodsof preparing solid porous oxide catalysts known in the art. Such methodsinclude mixing of the powdered nongel components, coprecipitation of thecomponents as gel, and impregnation of the carrier material, 1. e.,aluminum oxide, with an aqueous solution of a salt of the other metal,with subsequent ignition to the oxide. An example of the latter methodof preparation is the use of an aqueous solution of a molybdenum salt,preferably ammonium molybdate, to impregnate a porous alumina carrier,suitably in the form of small pellets, followed by ignition tomolybdenum oxide by passing an oxygen-containing gas over the catalystat a moderately' elevated temperature. Catalysts of the invention mayalso be prepared by coprecipitating the hydrous oxides from mixedaqueous solutions of their salts so as to form a composite with lessthan the desired amount of oneor more of the constituents and, afterforming the composite into pellets, adding the remainder of saidconstituent by single or multiple impregnation with a suitable saltsolution followed by calcination to convert to the oxide. The catalystmay be used in the form of granules of approximately 5 to 60 mesh size,in the form of pills or pellets, in the form of fluidized powder, or inthe form of dust suspended izi'the feed. In the operatic of the presentinvention the paraffin feed, e. g., normal butane, is admixed with steamin the ratio of between 1 to l and 1 to 30. The mixture is heated to theconversion temperature and passed into contact with the catalyst. Theeiiluent from the dehydrogenation zone may be processed in known mannerfor the separation of substantially pure olefins and diolefins. Theolefins may be separately dehydrogenated in a known manner forconversion to diolefins. Unconverted parafllns are recycled to thedehydrogenation step. If desired, the diolefins may be separated fromthe eiiluent and the fin at a temperature slightly below the desiredreous'volumes (S. T. P.) per volume oi. catalyst per hour. Thehydrocarbon and the steam may be mixed before charging to the reactionzone or the steam may be separately injected at a plurality of pointsalong the reaction zone. The steam is preferably preheated to atemperature at least as high as the temperature employed in the reactionand in some cases it may bepreferable to separately preheat thehydrocarbons and the steam before mixing. It is sometimes desirable topreheat the steam to a temperature somewhat above the desired conversiontemperature and to admix the preheated steam with preheated parafand soforth. When the activity of the catalyst becomes undesirably low becauseof carbon depositions, the flow of hydrocarbons is interrupted, andsteam is allowed to contact the catalyst until the carbon is removed.Air may be added to the steam during the regeneration period if desired.

In order to illustrate specific advantages of the invention, threecatalysts containing minor amounts of alumina and major amounts of thedehydrogenating metal oxides disclosed, and one of the catalysts of theaforementioned application containing a major amount of alumina wereutilized under comparable reaction conditions in a butanedehydrogenation process in the presence of considerable steam. All ofthe catalysts were in the form of one-eighth inch by one-eighth inchcylindrical pellets. In the several runs the steam was admixed withnormal butane, the mixture preheated to the conversion temperature andpassed over the pelleted catalyst. The effluent was condensed andanalyzed. The space velocity is expressed in terms of volumes of normalbutane per volume of catalyst per hour. The total conversion per passrepresents the percentage by volume of normal butane reacted in passingover the catalyst. The yield of normal butylenes and butadiene per passrepresents the percentage by volume of the normal butane feed which wasconverted to these products in passing over the catalyst. The ultimateyield indicates the percentage by volume of normal butane reacted whichwas 50 The compositions of the catalysts shown in Table I are asfollows: Catalyst A consisted 01' alumina, 30% vanadia, and 10% chromia.(All per cents are by weight.) Catalyst B con sisted of 25% alumina, 50%chromia, and 25% vanadia. Catalyst C consisted of 42% alumina, 40%chromia, and 18% vanadia. Catalyst D consisted of 38% alumina, 47%chromia, and 15% vanadia. All of the catalyst composite of catalysts Aand B and the major portion of the the catalysts C and D were preparedby precipitating the hydrous oxides from mixed solutions of chromium andaluminum nitrates and vanadium pentoxide dissolved in hydrogen peroxideby addition of 3 per cent aqueous ammonia followed by recovering theprecipitate and treating in the usual manner in order to form thecomposite into pills consisting of the metal oxides. Catalyst C was madeby impregnating the coprecipitated composite in the form of pelletsthree times with 30 per. cent chromium trioxide solution so as todeposit 23 per cent of chromium oxide; and catalyst D was made in asimilar mannor by impregnating six times with 30 per cent chromiumtrioxide solution so as to deposit an additional 37 per cent chromiumoxide thereon.

The rates oi. activity decline oi the various catalysts tested duringthe dehydrogenation cycle are shown in Table II.

Table II Catalyst Activity During Cycle; Time in Hours After Start 0!Cycle Catalyst 0.5 hr. 2 hrs. 4 hrs. 6 hrs. 8 hrs.

The catalyst activity readings in the above table are those recorded bya thermal-conductivity hydrogen-sensitive gas analyzer and 211178approximately 2-5 units above the total hydrocarbon convers on.

It can be seen from the data in Table I that the efliciency of thecatalysts of this invention containing minor amounts of the aluminumoxide compare very favorably with similar compositions which include amajor amount of alumina in their composition. It should also be notedthat the amount of conversion to butadiene is considerably higher forthe lower content alumina catalysts. However, the outstanding advantageof the catalysts of the invention in the dehydrogenation of paraflinhydrocarbons to olefins and diolefins in the presence of relativelylarge proportions of steam is shown in the data in Table II, whichclearly indicate that catalysts containing minor amounts of alumina incombination with the dehydrogenating metal oxides have at least as highinitial activity and maintain their activity at a high level over longerdehydrogenation periods than catalysts containing a major amount ofalumina and the same Table I 5 Yield of m v01. Total mama-elm, Per Centoi Temp., y Ratio Convsr- Mo] Per Cent 04H. Catalyst F. Steam to sion,in

" Butane Per Cent CH|+nCH| J per pass ultimate 722 18.8 24. 22 14. 8261.19 26. s 719 18.9 25. 29 1s. 66 e1. 02 40. 2 car 20. 2 23. 4s 1s. 005.5. 31 27. 2 730 18. 7 20. e4 10. as 53. 20 40. a

metal oxide dehydrogenating catalyst. This is a highly desirablecharacteristic since the onstream dehydrogenating cycle can besubstantially increased so as to reduce the number 01' regenerationperiods required and, therefore, substantially increase the yield perday from a given amount of catalyst.

Certain modifications of the invention wi1 become apparent to thoseskilled in the art and the illustrative details disclosed are not to beconstrued as imposing unnecessary limitations on the invention.

I claim:

1. A process for the dehydrogenation of an aliphatic paramn hydrocarbonwhich comprises contacting said hydrocarbon diluted with from 1 to 30volumes of steam per volume of hydrocarbon under dehydrogenatingconditions, including a temperature within the range 01' 1000 F. to 1400F. with a catalyst consisting essentially of alumina in the range of 10to 45 weight per cent of the catalyst and the balance of at least oneoxide selected from the group consisting of molybdenum oxide, tungstenoxide, and vanadium oxide.

2. The process of claim 1 in which the catalyst also contains at least 5weight percent chromium oxide.

3. A process for the dehydrogenation of an allphatic parafiinhydrocarbon containing from four to five carbon atoms per molecule whichcomprises passing said hydrocarbon in admixture with from 1 to 30volumes of steam per volume of hydrocarbon under dehydrogenatingconditions, including a temperature within the range of 1000 F. to 1400F. into contact with a catalyst consisting essentially of aluminum oxidein the range of to 45 weight per cent and the balance of chromia and atleast one oxide selected from the group consisting oi molybdenum oxide,tungsten oxide, and vanadium oxide.

4. The process of claim 1 in which said catalyst includes at least 5weight per cent vanadia.

5. The process of claim 1 in which said catalyst includes at least 5weight percent molybdena. 6. The process of claim 3 in which saidcatalyst includes at least 5 weight per cent vanadia.

7. The process of claim 3 in which said catalyst includes at least 5weight per cent molybdena.

8. A process for the dehydrogenation of an allphatic parafllnhydrocarbon containing from four to five carbon atoms per molecule whichcomprises passing said hydrocarbon in admixture with from vanadiumoxide.

JOHN W. MYERS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,406,646 Webb et al Aug. 27,1946 2,423,163 Thomas July 1, 1947 2,477,740 Grote Aug. 2, 19492,500,920 Pague et a1 Mar. 21, 1950 FOREIGN PATENTS Number Country Date115,967 Australia Oct. 15, 1942

1. A PROCESS FOR THE DEHYDROGENATION OF AN ALIPHATIC PARAFFINHYDROCARBON WHICH COMPRISES CONTACTING SAID HYDROCARBON DILUTED WITHFROM 1 TO 30 VOLUMES OF STEAM PER VOLUME OF HYDROCARBON UNDERDEHYDROGENATING CONDITIONS, INCLUDING A TEMPERATURE WITHIN THE RANGE OF1000* F. TO 1400* F. WITH A CATALYST CONSISTING ESSENTIALLY OF ALUMINAIN THE RANGE OF 10 TO 45 WEIGHT PER CENT OF THE CATALYST AND THE BALANCEOF AT LEAST ONE OXIDE SELECTED FROM THE GROUP CONSISTING OF MOLYBDENUMOXIDE, TUNGSTEN OXIDE, AND VANADIUM OXIDE.